public async Task WriteXmlAsync(string fileName, string xmlStr)
        {
            if (!DataFilesStorage.Exists(fileName))
            {
                await CreateDataFileAsync(fileName);
            }

            var cusXmlDoc = new XmlDocument();

            cusXmlDoc.LoadXml(xmlStr);

            using var ws         = DataFilesStorage.GetWriteStream(fileName);
            using var bufferedSt = new BufferedStream(ws, FilesIoOptions.BufferSize);

            var cTag   = string.Concat("</", XmlDataFileNodeNames.Root, ">");
            var buffer = Encoding.UTF8.GetBytes(cusXmlDoc.DocumentElement.InnerXml);

            bufferedSt.Position = ws.Length - cTag.Length;
            await bufferedSt.WriteAsync(buffer);

            await bufferedSt.WriteAsync(Encoding.UTF8.GetBytes(cTag));
        }
 public bool Exists(string fileName)
 {
     return(DataFilesStorage.Exists(fileName));
 }